The present invention relates to a paving apparatus for applying asphalt mixtures to a surface. More specifically, the apparatus is a portable drag box that includes a pugmill and an adjustable strike blade. It is especially useful for applying cold mix.
While screeds are commonly used to smooth hot mix paving material as it is applied, cold mix paving material is typically too viscous for conventional screeds to properly smooth the applied material. The screeds tend to grab and pull the viscous mix as it is being applied.
Conventional adjustment mechanisms for screeds simply change the tilt or angle of attack of the screed but do not raise or lower the screed. Thus, in order to continue to lay a planar surface when the stiffness of the paving mixture increases, the forward speed of the screed must be slowed or the angle of attack of the screed must be adjusted. Even in doing either or both, the ride of the finished pavement is compromised.
Additionally, conventional screeds simply float on the applied pavement material. While the weight of the screed itself tends to cause the screed to float in a downward direction, the upward force induced by the applied pavement material tends to force the screed back upward. Thus, the screed tends to simply follow the contour of the roadway surface regardless of whether that surface is planar. Furthermore, conventional screeds are typically rigidly attached to a prime mover that pulls the screed across the paving material. Thus, vertical movement of the prime mover is transferred to the screed, which can cause unwanted elevational changes to be created in the paved surface.
Some screeds are manually adjusted in response to elevational changes in the surface. However, the lag time between the detection of a non-planar condition and the actual adjustment of the screed is too great with manual adjustment. Thus, the adjustment often actually exaggerates the detected non-planar condition by accounting for the non-planar condition of the surface only after the screed has passed that area. This creates more severe raised sections and indentations in the surface.
Similar to screeds, the strike blades of drag boxes are traditionally adjusted manually. Again, the lag time between the detection of a non-planar surface and the actual adjustment of the blade tends to create more severe raised sections and indentations in the surface. In addition, manual adjustment of the strike blade is costly as an additional operator must stand on the grate of the drag box to adjust the strike blade while other operators operate the prime mover that pulls the drag box. There is a need in the industry to lay a more planar road with a drag box.
In order to overcome these disadvantages, a device for evening out asphalt mixtures placed on a surface having high and low elevations is needed. More specifically, this device should be significantly more responsive to changes in the elevation of the surface than conventional devices.